1. Field of the Invention
This invention relates to a toner for developing an electrostatic image in an image-forming process such as electrophotography or electrostatic printing, or a process for producing a toner for forming a toner image in a toner-jet type image-forming method. More particularly, this invention relates to a process for producing a toner used in a fixing method in which a toner image formed using the toner is fixed to a transfer medium such as a printing sheet under application of heat and pressure.
2. Related Background Art
In order to render visible an electric or magnetic latent image formed on a recording member, an image-forming method is available in which electroscopic or magnetosensitive fine particles called a toner are attracted to the latent image to form a visible image. It may typically include electrophotography, and a number of methods are known as methods therefor as disclosed in, e.g., U.S. Pat. No. 2,297,691. In this electrophotography, copies are commonly obtained by forming an electrostatic latent image on a photosensitive member by various means, utilizing a photoconductive material, subsequently developing the latent image by the use of a toner to form a toner image, transferring the toner image to a transfer medium such as paper as occasion calls, and thereafter fixing the toner image to the transfer medium by the action of heat, pressure or solvent vapor.
In recent years, the above technique has become used in output means, i.e., what is called printers, of computers, word processors and so forth because of its high image quality and stillness. Usually, toners used in printers and copying machines are fine particles composed chiefly of a resin, a colorant such as a magnetic material, carbon black, a dye or a pigment and a wax, and have particle diameters usually ranging from 6 to 30 xcexcm. Toners are commonly produced by mixing and melting a colorant comprising a dye or pigment or a magnetic material in a thermoplastic resin to disperse the colorant uniformly therein, followed by fine pulverization and classification to obtain toners having a desired particle diameter. This method is stable as a technique, and enables relatively easy management of materials and production steps.
Meanwhile, a method of producing a toner by polymerization, in particular, a method of producing a toner by what is called suspension polymerization is proposed. Such a method is disclosed in, e.g., Japanese Patent Publication Nos. 36-10231 and 51-14895 and Japanese Patent Application Laid-Open Nos. 53-17735, 53-17736 and 53-17737. This method is a method in which a binder resin and materials to be incorporated in the toner, including a colorant such as a dye or a pigment (e.g., a magnetic material or carbon block), a charge control agent, and a release agent such as wax or silicone oil, are dissolved or dispersed in a polymerizable monomer optionally together with a polymerization initiator and a dispersant to prepare a polymerizable composition, which is then dispersed in an aqueous continuous phase containing a dispersion stabilizer by means of a dispersion apparatus to form a dispersion of fine particles, and this dispersion is polymerized and then solidified to obtain toner particles having any desired particle diameter and composition. This method has no pulverization step, and is expected to bring about the effect of energy saving, improvement in process yield and cost reduction.
As a method of improving print quality, studies are energetically made on a technique by which the latent image can faithfully be reproduced by making the particle diameter of the toner smaller. However, making the particle diameter smaller makes the quantity of toner per unit are smaller, and hence the coloring power per unit volume of the toner must be made higher in order to attain the desired image density. As a means therefor, it is common to use a means by which the colorant dye or pigment is introduced in a larger quantity. There, however, is a problem that pigments, in particular quinacridone pigments, used as colorants of toners are no expensive as to result in an increase in the production cost. Accordingly, in order to make the coloring power of dyes and pigments themselves higher and improve the transparency of OHP images, studies are energetically made on how the dispersion of dyes and pigments in the interior of toner particles be improved.
In order to improve the dispersion of dyes and pigments, it is commonly important to make the dyes and pigments readily compatible with resins. Accordingly, the dyes and pigments are subjected to surface treatment. Proposals on the surface treatment of dyes and pigments to improve their dispersibility are disclosed in Japanese Patent Application Laid-open No. 11-119461, Japanese Patent No. 2800558 and so forth. There, however, has been room for improvement with regard to the dispersibility of pigments.
In the case of pulverization toners, the surface treatment of dyes and pigments must be regulated in conformity with the composition of binder resins, and there has been a problem that any good state of dispersion can not be attained if the matching of the both is improper.
In the case of polymerization toners, the surface treatment of dyes and pigments is made in many cases, most of which, however, is to make hydrophobic treatment with silane coupling agents or to make a pigment dispersant (which is a polymer having a polar group) adsorbed on the particle surfaces of a colorant so that the pigment can be prevented from agglomerating.
In the case when such a pigment dispersant is used, the state of dispersion to a certain extent can be achieved. However, the pigment may undergo re-agglomeration in post steps of drying, shaping, polymerization reaction and so forth, or, in the production of polymerization toner in an aqueous medium, the presence of polar groups on the pigment particle surfaces may cause the migration of pigment to toner particle surfaces, resulting in a lowering of charging performance and environmental stability.
Accordingly, an object of the present invention is to provide a toner having solved the above problems, and a process for producing the toner.
More specifically, an object of the present invention is to provide a toner having superior coloring powder and transparency, and a process for producing such toner.
Another object of the present invention is to provide a toner having a pigment added in a small quantity, and having achieved a cost reduction, and a process for producing such toner.
Still another object of the present invention is to provide a toner which does not cause any migration of pigment to toner particle surfaces and has superior charging performance and environmental stability, and a process for producing such toner.
To achieve the above objects, the present invention provides a toner containing at least a binder resin, a pigment and a pigment dispersant:
the pigment dispersant having a structure represented by the following Formula (1): 
wherein at least one of R1 and R2 is a substituent X1 represented by 
where Y1 is an oligomer or a polymer, and the other is a hydrogen atom.
The present invention also provides a toner containing at least a binder resin, a pigment and a pigment dispersant;
the pigment dispersant having a structure represented by the following Formula (2): 
wherein at least one of R3 and R4 is a substituent X2 represented by 
where Y3 and Y4 are each a substituent selected from the group consisting of H, CH3, an oligomer and a polymer,
and the other is a hydrogen atom.
The present invention still also provides a process for producing the above toner.
The pigment dispersant according to the present invention has a structure wherein a quinacridone molecular skeleton which is readily adsorptive on the colorant pigment and an oligomer or polymer which has good affinity for the solvent and for the resin serving as a toner binder are covalently bonded. Also, in the pigment dispersant according to the present invention, the substituents X1 and X2 have an affinity for the polymerizable monomer used in a pigment dispersion step and for the resin serving as a toner binder, and hence the pigment dispersant may become liberated with difficulty in the polymerizable monomer or in the resin, and can exist stably.
The pigment dispersant that can be used in the present invention has the structure of Formula (1) or (2). In Formula (1) at least one of R1 and R2 is a substituent X2. If the substituent X1 is in a large number, it on the one hand strengthens the affinity for the solvent, but on the other hand may inhibit the adsorptive force to the pigment. Accordingly, it is preferred that one is the substituent X1 and the other is a hydrogen atom. Similarly, in Formula (2), too, at least one of R3 and R4 is a substituent X2, preferably one is the substituent X2, and the other is a hydrogen atom.
The substituent X1 has a substituent Y1, and substituent X2 has substituents Y2 and Y3. The substituents Y1, Y2 and Y3 that can be used in the present invention may be any conventional oligomers or polymers. In particular, a vinyl polymer component containing as a monomer unit a monomer selected from the group consisting of styrene, a styrene derivative, acrylic or methacrylic acid and an acrylic or methacrylic acid derivative, or a polyester component is effective. These substrates are required to have good affinity for the solvent used in a pigment dispersion step and for the resin serving as a toner binder.
The oligomer or polymer constituting the substituents Y1, Y2 and Y3 may specifically include polystyrene, poly-xcex1-methylstyrene, polyacrylate, polymethacrylate, a styrene-acrylate copolymer, a styrene-methacrylate copolymer, a styrene-glycidyl acrylate copolymer, a styrene-glycidyl methacrylate copolymer, and polyester. Also, the substituents Y1, Y2 and Y3 may each preferably have a number-average molecular weight of from 500 to 100,000, and more preferably from 500 to 30,000, and may preferably have a sharp molecular weight distribution, taking account of the solubility in the solvent used in a pigment dispersion step. The molecular weight of the substituents Y1, Y2 and Y3 can be controlled by regulating the molecular weight of the oligomer or polymer used, when the oligomer or polymer is introduced as the substituent into the compound having the quinacridone skeleton.
In the present invention, the pigment dispersant may be used in an amount of from 2 to 100 parts by weight, based on 100 parts by weight of the binder resin. In the case when the toner is produced by polymerization, it may preferably be used in an amount of from 3 to 30 parts by weight.
In the production of the toner of the present invention, known formulation, i.e., a pigment, a resin and other additives such as a wax and a charge control agent may be used except that the pigment dispersant of Formula (1) or (2) is contained. As methods for the production, known methods may also be used. Where the toner is produced by pulverization, the pigment dispersant may be mixed together with a binder resin, a pigment and other additives, and the mixture obtained may be melt kneaded under application of heat and mechanical shear force, followed by a polymerization step and a classification step to produce a toner. In the case of the pulverization, the pigment may previously be treated with the pigment dispersant, and the melt kneading may be carried out using such a pigment to produce the toner.
As another method, the toner may also be produced by a polymerization process in which toner particles are directly obtained by polymerizing a polymerizable monomer in an aqueous medium, and the toner may be obtained by suspension polymerization, emulsion polymerization or emulsification agglomeration. In the process for producing the toner by suspension polymerization, the pigment dispersant and optionally the resin may be dissolved into part or the whole of the polymerizable monomer, and pigment powder may be added little by little with stirring to make it fit well to the polymerizable monomer, where mechanical shear force is further applied by means of a dispersion machine such as a ball mill or a paint shaker, a dissolver, an attritor, a sand mill, a high-speed mill to produce a pigment-dispersed paste. The pigment-dispersed paste thus obtained, a polymerization initiator and the remaining polymerizable monomer may be mixed to make up a polymerizable monomer composition, which is then added to an aqueous medium containing a dispersion stabilizer to carry out granulation and then polymerization to obtain toner particles. In the case of polymerization, the pigment and the pigment dispersant may separately be added and then mixed when the polymerizable monomer composition is prepared.
The polymerizable monomer that can be used when the toner of the present invention is produced by polymerization is an addition polymerization or condensation polymerization type monomer. It may preferably be an addition polymerization type monomer. It may specifically include styrene; styrene derivatives such as o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrenee, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene and p-n-dodecylstyrene; unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; unsaturated polyenes such as butadiene and isoprene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl iodide; vinyl esters such as vinyl acetate, vinyl propionate and vinyl benzoate; xcex1-methylene aliphatic monocarboxylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate and phenyl acrylate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and isobutyl vinyl other; vinyl ketones such as methyl vinyl ketone, hexyl vinyl ketone and methyl isopropenyl ketone; N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrrolidone; vinylnaphthalenes; and acrylic or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide.
The binder resin used when the toner of the present invention is produced by pulverization is selected chiefly taking account of the affinity for the substituent X1 or X2. For example, if may include polystyrene, poly-xcex1-methylstyrene, polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, a styrene-acrylate copolymer, a styrene-methacrylate copolymer, and polyester.
As the pigment that can be used in the present invention, any known pigments may be used. In particular, color pigments such as quinacridone pigments, carbon black and phthalocyanine pigments may preferably be used. For example, they may include Pigment Violet 19, Pigment Red 122, Pigment Red 207, Pigment Red 206, Pigment Red 202, Pigment Black 6, Pigment Black 7, Pigment Black 8, Pigment Black 10, Pigment Blue 16, Pigment Blue 15, Pigment Blue 15:1, Pigment Blue 15:2, Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 15:5, Pigment Blue 15:6, Pigment Green 7 and Pigment Green 36.
In the present invention, the pigment may preferably be added in an amount of from 3 to 20 parts by weight based on 100 parts by weight of the binder resin or polymerizable monomer.
The polymerization initiator used in the production process for the toner of the present invention may include known polymerization initiator. Stated specifically, it may include azo compounds such as 2,2xe2x80x2-azobisisobutyonitrile, 2,2xe2x80x2-azobis-(2,4-dimethylvaleronitrile), 2,2xe2x80x2-azobis(2-methylbutyronitrile, 1,1xe2x80x2-azobis-(cyclohexane-1-carbonitrile), dimethyl-2,2xe2x80x2-azobisisobutyrate, 4,4xe2x80x2-azobis-4-cyanovaleric acid, and 2,2xe2x80x2-azobis(4-methoxy-2,4-dimethylvaleronitrile); peroxides such as benzoyl peroxide, and methyl ethyl ketone peroxide; nucleophilic reagents such as alkali metals, metal hydroxides and Grignard reagents; and protonic acid, metal halides and stabilized carbonium ions. The polymerization initiator may preferably be in a concentration of from 0.1 to 20% by weight, and more preferably from 0.1 to 10% by weight, based on the weight of the polymerizable monomer.
In the case when the toner of the present invention is produced by polymerization, a chain transfer agent may be used, which may include known chain transfer agents.
In the present invention, toner additives as shown below may further be used in order to provide the toner with various properties.
In order to stabilize triboelectric charging performance of the toner, a charge control agent may be incorporated in the toner. In this case, it is preferable to use a charge control agent having a high toner charging speed and capable of maintaining a constant charge quantity stably. When the polymerization method is used to produce the toner particles, charge control agents having no polymerization inhibitory action are particularly preferred. Stated specifically, as negative charge control agents, preferred are metal compounds of salicylic acid, alkyl salicylic acids, dialkyl salicylic acids, naphthoic acid or dicarboxylic acids, polymer type compounds having sulfonic acid or carboxylic acid in the side chain, boron compounds, urea compounds, silicon compounds and carixarene. As positive charge control agents, preferred are quaternary ammonium salts, polymer type compounds having such as quaternary ammonium salt in the side chain, guanidine compounds, and imidazole compounds. Any of these charge control agents may preferably be added in a amount of from 0.5 to 10 parts by weight based on 100 parts by weight of the binder resin.
It is also preferable to add to the toner, external additives such as a fluidity-providing agent, an abrasive, a lubricant and charge controlling particles.
As the fluidity-providing agent, metal oxides such as silicon oxide, aluminum oxide and titanium oxide may preferably be used. These may more preferably these having been subjected to hydrophobic treatment. As the abrasive, metal oxides such as cerium oxide, aluminum oxide, magnesium oxide and chromium oxide, nitrides such as silicon nitride, carbides such as silicon carbide, and metal salts such as strontium titanate, calcium sulfate, barium sulfate and calcium carbonate may preferably be used. As the lubricant, fluorine resin powders such as vinylidene fluoride and polytetrafluoroethylene, and fatty acid metal salts such as zinc stearate and calcium stearate may preferably be used. As the charge controlling particles, metal oxides such as tin oxide, titanium oxide, zinc oxide, silicon oxide and aluminum oxide, and carbon black may preferably be used.
Any of these external additives may be used in an amount of from 0.1 part to 10 parts by weight, and preferably from 0.1 part to 5 parts by weight, based on 100 parts by weight of the toner particles. These additives may be used alone or in combination of two or more types.
The toner of the present invention may be used as a one-component developer, or may be blended with a carrier so as to be used as a two-component developer.
In the present invention, various physical properties are measured in the manner described below.
The molecular weight distribution of the resin component contained in the toner of the present invention and that of the polymer composition (resin component) soluble in the polymerizing solvent used in the present invention are measured with a GPC measuring instrument (HLC-8120GPC, manufactured by Toso Co.) under the following conditions.
Measuring conditions:
Columns: TSKgelHM-M (6.0 mm in diameterxc3x9715 cm), combination of two columns.
Temperature: 40xc2x0 C.
Flow rate: 0.6 ml/min.
Detector: RI.
Sample concentration: 1.0 xcexcl of 0.1% sample.
To prepare the sample, the sample to be measured is put in THF (tetrahydrofuran), which is then left for several hours, followed by thorough shaking (until no coalesced matter comes to be seen), and the mixture is further left to stand still for 12 hours. Then, the mixture is passed through a sample-treating filter (pore size of 0.45 xcexcm), and the resultant filtrate is used as the sample for GPC measurement. As a calibration curve, a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample is used.
The toner and the carrier are blended in a suitable blend quantity (2 to 15% by weight) when a developer is produced, and are blended with a Turbra mixer for 180 seconds, and this blended powder (developer) is put in a container made of a metal at the bottom of which a conductive screen with an opening of 20 xcexcm (635 meshes) is provided, and then sucked by means of a suction device. The triboelectric charge quantity is determined from the difference in weight before and after the suction and from the potential accumulated in a capacitor connected to the container. Here, suction pressure is set at 250 mmHg. By this method, the triboelectric charge quantity (Q) is calculated according to the following expression.
Q(xcexcC/g)=(Cxc3x97V)/(W1xe2x88x92W2) 
wherein W1 is the weight before suction, W2 is the weight after suction, C is the capacity of the capacitor, and V is the potential accumulated in the capacitor.
To 100 to 150 ml of an electrolytic solution, 0.1 to 5 ml of a surface active agent (alkylbenzene sulfonate) is added, and 2 to 20 mg of the sample to be measured is added thereto. The electrolytic solution in which the sample has been suspended is subjected to dispersion for about 1 minute to about 3 minutes by means of an ultrasonic dispersion machine. Particle size distribution of toner particles of 2 to 40 xcexcm diameters is measured on the basis of volume, by means of Coulter Counter Multisizer, using an aperture of 100 xcexcm. Number-average particle diameter and weight-average particle diameter measured are calculated from the results obtained.